The term 'Variable Star' originally referred to those stars that vary in their brightness. All stars vary in one way or another. There are about 20,000 recognized variable stars listed in the well-known Catalogue of Variable Stars (See bibliography). The major types of variable stars are listed below.

Pulsating Variables

Number

Explosive Variables

Number

C

Classical Cepheids

696

N

Novae

203

I (L)

Irregular Variables

1687

Ne

Nova-lie Variables

M

Mira Ceti

4600

SN

Supernovae

7

SR

Semi-regular Variables

4423

RCB

R Cr Borealis Stars

31

RR

RR Lyrae Variables

4423

RW (I)

RW Aur, T Tauri Stars

1005

RV

RV Tauri Stars

100

UG

U Geminorum Stars

210

C

Cephei Stars

14

UV

UV Ceti (flare) Stars

100

SC

Scuti Stars

12

Z

Z Camelopardalis Stars

19

CV

CVn Stars 28

Eclipsing variables of all kinds total 4018. The more recent designations in the above table are in parenthesis. Individual variable stars within each constellation are named by letters and numbers that indicate their order of discovery. The first variable found within any constellation has the letter R assigned to it (example: R Coronae Borealis). Subsequently discovered variables take the letters S, T ... to Z; then RR, RS, RT ... SS, ST, and so on through ZZ.

After ZZ, variable stars are named starting from the beginning of the alphabet with AA, AB, AC ... through AZ, then BB, BC through BZ, and son on through QZ.

The preceding will take care of 344 stars in each of the constellations. If there are still more variables, they receive numbers from 335 on, preceded by the letter 'V' and followed by the constellation. An example would be V 335 Cygni, being the 335th variable star discovered in the constellation Cygnus.